scsi: fnic: fix invalid stack access

gcc -O3 warns that some local variables are not properly initialized:

drivers/scsi/fnic/vnic_dev.c: In function 'fnic_dev_hang_notify':
drivers/scsi/fnic/vnic_dev.c:511:16: error: 'a0' is used uninitialized in this function [-Werror=uninitialized]
  vdev->args[0] = *a0;
  ~~~~~~~~~~~~~~^~~~~
drivers/scsi/fnic/vnic_dev.c:691:6: note: 'a0' was declared here
  u64 a0, a1;
      ^~
drivers/scsi/fnic/vnic_dev.c:512:16: error: 'a1' is used uninitialized in this function [-Werror=uninitialized]
  vdev->args[1] = *a1;
  ~~~~~~~~~~~~~~^~~~~
drivers/scsi/fnic/vnic_dev.c:691:10: note: 'a1' was declared here
  u64 a0, a1;
          ^~
drivers/scsi/fnic/vnic_dev.c: In function 'fnic_dev_mac_addr':
drivers/scsi/fnic/vnic_dev.c:512:16: error: 'a1' is used uninitialized in this function [-Werror=uninitialized]
  vdev->args[1] = *a1;
  ~~~~~~~~~~~~~~^~~~~
drivers/scsi/fnic/vnic_dev.c:698:10: note: 'a1' was declared here
  u64 a0, a1;
          ^~

Apparently the code relies on the local variables occupying adjacent memory
locations in the same order, but this is of course not guaranteed.

Use an array of two u64 variables where needed to make it work correctly.

I suspect there is also an endianness bug here, but have not digged in deep
enough to be sure.

Fixes: 5df6d73 ("[SCSI] fnic: Add new Cisco PCI-Express FCoE HBA")
Fixes: mmtom ("init/Kconfig: enable -O3 for all arches")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200107201602.4096790-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/fnic/vnic_dev.c

@@ -688,26 +688,26 @@ int vnic_dev_soft_reset_done(struct vnic_dev *vdev, int *done)
 
 int vnic_dev_hang_notify(struct vnic_dev *vdev)
 {
-	u64 a0, a1;
+	u64 a0 = 0, a1 = 0;
 	int wait = 1000;
 	return vnic_dev_cmd(vdev, CMD_HANG_NOTIFY, &a0, &a1, wait);
 }
 
 int vnic_dev_mac_addr(struct vnic_dev *vdev, u8 *mac_addr)
 {
-	u64 a0, a1;
+	u64 a[2] = {};
 	int wait = 1000;
 	int err, i;
 
 	for (i = 0; i < ETH_ALEN; i++)
 		mac_addr[i] = 0;
 
-	err = vnic_dev_cmd(vdev, CMD_MAC_ADDR, &a0, &a1, wait);
+	err = vnic_dev_cmd(vdev, CMD_MAC_ADDR, &a[0], &a[1], wait);
 	if (err)
 		return err;
 
 	for (i = 0; i < ETH_ALEN; i++)
-		mac_addr[i] = ((u8 *)&a0)[i];
+		mac_addr[i] = ((u8 *)&a)[i];
 
 	return 0;
 }
@@ -732,30 +732,30 @@ void vnic_dev_packet_filter(struct vnic_dev *vdev, int directed, int multicast,
 
 void vnic_dev_add_addr(struct vnic_dev *vdev, u8 *addr)
 {
-	u64 a0 = 0, a1 = 0;
+	u64 a[2] = {};
 	int wait = 1000;
 	int err;
 	int i;
 
 	for (i = 0; i < ETH_ALEN; i++)
-		((u8 *)&a0)[i] = addr[i];
+		((u8 *)&a)[i] = addr[i];
 
-	err = vnic_dev_cmd(vdev, CMD_ADDR_ADD, &a0, &a1, wait);
+	err = vnic_dev_cmd(vdev, CMD_ADDR_ADD, &a[0], &a[1], wait);
 	if (err)
 		pr_err("Can't add addr [%pM], %d\n", addr, err);
 }
 
 void vnic_dev_del_addr(struct vnic_dev *vdev, u8 *addr)
 {
-	u64 a0 = 0, a1 = 0;
+	u64 a[2] = {};
 	int wait = 1000;
 	int err;
 	int i;
 
 	for (i = 0; i < ETH_ALEN; i++)
-		((u8 *)&a0)[i] = addr[i];
+		((u8 *)&a)[i] = addr[i];
 
-	err = vnic_dev_cmd(vdev, CMD_ADDR_DEL, &a0, &a1, wait);
+	err = vnic_dev_cmd(vdev, CMD_ADDR_DEL, &a[0], &a[1], wait);
 	if (err)
 		pr_err("Can't del addr [%pM], %d\n", addr, err);
 }